Replace some src/s undefs by never even checking on relevant platforms

Replace some src/s undefs by never even checking on relevant platforms

* configure.in: (getwd): Don't check for it on unixware.
(random, rint): Don't check for these on hpux.
(res_init, libresolv): Don't check for these on darwin.

* src/s/darwin.h (HAVE_RES_INIT, HAVE_LIBRESOLV):
* src/s/hpux10-20.h (HAVE_RINT, HAVE_RANDOM):
* src/s/unixware.h (HAVE_GETWD): Move undefs to configure (effectively).